1. Field of the Invention
The present invention relates to a method of fabricating a hermetic terminal and a hermetic terminal, a method of fabricating a piezoelectric oscillator and a piezoelectric oscillator, an oscillator, an electronic appliance, and a radio clock.
2. Description of the Related Art
In recent years, mobile telephones and portable information terminal devices employ a piezoelectric oscillator using quartz crystal as a time source, a timing source of control signals, and a reference signal source. As this type of piezoelectric oscillator, various ones are offered. As one of them, a cylinder package piezoelectric oscillator formed in a cylindrical shape is known.
As shown in FIG. 30, a piezoelectric oscillator 70 is configured to have a tuning fork piezoelectric vibrating piece 71, a case 72 in a cylindrical shape with a bottom in which the piezoelectric vibrating piece 71 is accommodated, and a hermetic terminal 73 that hermetically seals the piezoelectric vibrating piece 71 inside the case 72.
The hermetic terminal 73 is configured of an annular ring 74 formed of a metal material, two leads 75 arranged as they penetrate through the ring 74 and are individually joined to two mount electrodes 71a of the piezoelectric vibrating piece 71, and a filler 76 that fixes the leads 75 to the ring 74 in one piece in an insulating state and hermetically seals the inside of the case 72.
The two leads 75 each have an inner lead portion 75a that is the portion extended inside the case 72 and have an outer lead portion 75b that is the portion extended outside the case 72. Then, the outer lead portion 75b functions as an external connecting terminal.
In addition, the case 72 is pressed, fitted, and fixed to the outer side of the ring 74. Since the case 72 is press fitted under a vacuum atmosphere, the space surrounding the piezoelectric vibrating piece 71 inside the case 72 is hermetically sealed in the vacuum state.
In the piezoelectric oscillator 70 thus configured, a predetermined voltage is applied as drive voltage to each of the outer lead portions 75b of the two leads 75, and then current is carried from the inner lead portion 75a to the piezoelectric vibrating piece 71 through the mount electrode 71a. Thus, the piezoelectric vibrating piece 71 oscillates at a predetermined frequency.
This type of piezoelectric oscillator is mounted on various electronic appliances. However, since these electronic appliances are being reduced in size year after year, also in the piezoelectric oscillator, further size reduction is demanded. In order to reduce the size of the piezoelectric oscillator, it is effective to reduce the outer diameter of the ring. To this end, it is necessary to reduce the diameters of two leads. However, in the case in which the leads are made narrower than the current form, the stiffness is decreased, and then it is likely to deform the leads in the process of fabrication. Particularly, the outer lead portions that are longer than the inner lead portions tend to become deformed. When the outer lead portions become deformed, they cannot maintain themselves in the state of being parallel with each other. Thus, the quality is degraded, and the oscillator cannot be used as a product. Consequently, it is likely to cause a reduction in yields.
In addition, in the process of fabrication, the outer lead portions are entangled with the outer lead portions of another hermetic terminal, which might temporarily stop the production line. Also in this point, it is likely to cause a reduction in yields. Particularly, the more size reduction is aimed, the more the problems might occur noticeably. On this account, in the fabricating method under present conditions, it is difficult to fabricate a piezoelectric oscillator of high yields and high quality which can be further reduced in size. Particularly, it is difficult to fabricate a hermetic terminal configuring a piezoelectric oscillator.
Then, a piezoelectric oscillator is provided which has a hermetic terminal with a single lead, not two leads (see Patent Reference 1 (see JP-A-2002-43886)). This hermetic terminal has a projecting piece formed in one piece with a ring, and the projecting piece serves as the role of the inner lead portion before. In other words, the lead and the projecting piece are electrically connected to a piezoelectric vibrating piece. As described above, since the projecting piece formed in one piece with the ring is allowed to function as the inner lead portion, two leads, which are required before, can be reduced to a single lead.
On this account, even though the outer diameter of the ring is reduced, it is unnecessary to reduce the diameter of the lead as compared with the case of using two leads, a reduction in stiffness can be prevented, and the deformation of the lead can be prevented. In addition to this, since a single lead is provided, leads are unlikely to become entangled with each other in the process of fabrication, and thus the hermetic terminal can be reduced in size, and the piezoelectric oscillator can be reduced in size.
In addition, in the hermetic terminal which supports the piezoelectric vibrating piece inside the case including the hermetic terminal 73 of the piezoelectric oscillator 70 shown in FIG. 30 and the hermetic terminal described in the Patent Reference 1, in order to allow the size reduction of the piezoelectric oscillator as well as to ensure the reliability, it is necessary that the piezoelectric vibrating piece is arranged at the position closer to the center inside the case to reliably prevent the piezoelectric vibrating piece from contacting to the case. To this end, the inner lead is not eccentric to the ring and arranged so as to be positioned at the center of the ring. Then, one of the end parts of the inner lead portion supporting the piezoelectric vibrating piece is flattened to form a stair portion, and the stair portion holds the piezoelectric vibrating piece thereon.
In order to fabricate the piezoelectric oscillator provided with the hermetic terminal having the stair portion like this, for example, the lead is inserted into the ring through the filler, they are fired in this state to fix the lead inside the ring with the filler, the lead is flattened to form the stair portion, a bump is formed on the formed stair portion, and then the bump is used as an alignment mark to position the piezoelectric vibrating piece.
However, the method before still has the following problems.
As described above, since it is necessary to arrange the inner lead so that it is positioned at the center of the ring, it is demanded to more reliably prevent the inner lead from being eccentric. The eccentricity of the inner lead to the ring occurs when the filler is fired and the lead is fixed inside the ring. In other words, in the firing process, the ring, the filler, and the lead are joined to each other and accommodated in a firing jig, and then they are fired in this state. However, naturally, since the accommodating portion for the lead in the firing jig is slightly formed greater than the lead, the lead becomes unsteady in the accommodating portion. Then, the lead is unsteady and not arranged in parallel with the center axis of the ring or matched therewith, the lead is accommodated as it is tilted, and the lead is fired and fixed in this attitude, which might cause eccentricity.
In addition, in connecting the piezoelectric vibrating piece to the inner lead, as described above, the bump on the stair portion formed in the flattening process is used as the alignment mark for positioning, but the stair portion formed in the flattening process is a trapezoid, not a rectangle, and also uneven, not uniform. Therefore, the position of the bump formed here is also varied, and thus the piezoelectric vibrating piece positioned by using the bump as the alignment mark also has variations in the connecting position.
In addition, in the hermetic terminal described in Patent Reference 1, it is necessary to form the projecting piece in one piece with the ring. In addition to this, it is necessary to form the projecting piece on a part of the ring formed annular. However, this process is not easily to perform, which takes a lot of efforts and time. Particularly, since it is necessary to bend the projecting piece while the ring is prevented from being deformed in bending the projecting piece, productivity is not excellent. Therefore, actually, it is necessary to produce a large amount of hermetic terminals a day, but the hermetic terminal is not suited for such mass production.